The invention relates to a method according to the Oberbegriff of claim 1. Through this method, solids which are added for the analysis adjustment during the metal production, in particular steel production, in varying amounts outside of the actual metal-producing process, can be fed in a simple manner with a high accuracy in the analysis and a high output without using expensive auxiliary means like refractorily supplied lances or threading machines to the metal melts.
K. Scheidig et al discloses in xe2x80x9cStahl und Eisenxe2x80x9d (Steel and Iron), Volume 105, No. 25-26 of Dec. 16, 1985, Pages 1437-1441, a pneumatic injecting of coal dust through the blast tuyere of a blast furnace by dense flow conveyance. The coal dust is thereby injected into the melt in measured quantities.
DE-OS 24 08 363 discloses a method for introducing finely divided particles of an aggregate into a liquid metal melt, while the melt is removed from the melt container.
Because of the increasing demands by the customers regarding the maintaining of analysis regulations by the steel producer and simultaneously continuously increasing competitive pressures, secondary metallurgy, that is the treatment of the liquid metals following the actual metal production in a converter or electric-arc oven, has increasingly gained in importance within the past years. During the course of this development the method, through which fine-granular, fluid solids, as they are needed for adjusting the end analysis of the liquid metal, in particular, steel in varying amounts, are added to the metal melt, receive more and more importance with regard to the prediction of the output, the accuracy of the analysis, method expenses, operation safety and flexibility.
The methods, which are used today, are:
a) addition utilizing the force of gravity during the tapping by means of sliding, flowing or manual feeding;
b) addition to the bath surface in the pan by means of conveyor systems or manually;
c) threading of fill wires by means of threading machines;
d) injection by dipping in refractorily supplied dipping lances such as, for example, the TN-method.
The addition methods mentioned under a) and b) are characterized by not being exactly predictable, a comparatively low output and insufficient accuracy, which results in the necessity of an increased consumption of alloy media and, relatively often, a one-time or repeated correction of the added amount. If the addition is done manually, then additional personnel are needed and, at the same time, the degree of the reproducibility of the analysis results is then comparatively even less.
By comparison, the methods mentioned under c) and d) are distinguished by a comparatively high accuracy and high reproducibility. However, the high costs are disadvantageous.
These high costs are caused in the methods according to c) by the production costs of the fill wire needed for the threading, in the methods according to d) by the specific refractory costs of the injection lances, which have a much shorter life because of the existing temperatures and the necessary treatment duration than, for example, the pure flushing lances.
The injection methods are moreover characterized by expensive, personnel-intensive lance procedures.
Further disadvantages of the up to now used methods are that the amounts of alloy media, which can be added per unit of time, are limited by the technical boundary conditions, for example, during threading or injecting. In addition, the metal melt experiences during the treatment according to the method according to c) and d) a stronger cooling off, when threading in fill wires, it is necessary to additionally melt the surrounding metal envelope and during injection, heat is additionally radiated to the refractory material of the lance and to the transport gas.